1. Field of the Invention
The present invention relates to a lithium ion secondary battery confirming manufacturing quality and safety of the battery by restraining the internal short of the battery induced by the formation of dendrite within the battery.
2. Description of the Related Art
Generally, researches on development of a chargeable/dischargeable secondary battery in a high-tech field such as a digital camera, a cellular phone, a laptop computer, a hybrid vehicle, and the like are actively conducted different from a non chargeable primary battery.
The secondary battery includes a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, a lithium secondary battery, and the like. Among the batteries, the lithium secondary battery has an operation voltage of 3.6 V or above, and is used as a power source of a portable electronic device or of a hybrid vehicle of a high power by connecting the batteries in series. The lithium secondary battery has the operation voltage higher by three times than the nickel-cadmium battery or the nickel-metal hydride battery, and has good energy density properties per unit weight. Thus, the lithium secondary battery is used at a fast-growing rate.
For maintaining the manufacturing quality of the lithium secondary battery and using the battery safely for a long time, the internal short of the battery induced by dendrite formed at the surface of an anode by the reduction of copper ion (Cu2+) is necessary to be restrained. The copper ion is produced by the oxidation of copper foreign materials in the battery. In view of the manufacturing quality of a cell, defect ratios during manufacturing the cells may be increased by the dendrite generated from the reduction of metal ions during charging and discharging.
In addition, when the dendrite generated during the manufacturing makes an electric connection of a cathode and an anode due to external pressure or vibration, the safety and the stability of the cell during using may be deteriorated. During using the cell, the safety and the stability of the cell may be largely deteriorated due to the production of the dendrite by the reduction of additionally produced metal ions. Thus, the formation of the dendrite possibly making an electric connection between the cathode and the anode is necessary to be restrained in the lithium secondary battery.